Issac I have the same problem as yours. After plug in dc adapter, fans just spinning, but everything else is silent, no led, no chime.. How do You exactly burnt the motherboard? 15min pre warming in 180C? and then additionally 8mins?

Apple's Mac Mini is a desktop computer that differs from most of the company's other consumer models in that it lacks an integrated monitor. As with any computer, you may encounter the occasional software glitch that will render your Mac Mini unresponsive to input -- requiring a restart. A basic hard reset is enough to correct most problems, but if you encounter issues with your computer not powering up properly or failing to recover from sleep, a Power Management Unit or System Management Controller reset may prove necessary.

Basic Hard Reset

Step

Locate the power button, installed on the left side of the rear panel.

Step

Depress the power button until the computer powers down.

Step

Press the power button again to restart the computer.

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PMU Reset (PowerPC)

Step

Disconnect the Mac Mini's power cord, as well as any other cables that may be connected to the computer. Wait 10 seconds before proceeding.

Step

Hold down the computer's power button, then reconnect the power cord. Release the power button.

Step

Press the power button to turn on the computer.

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SMC Reset (Intel)

Step

Disconnect the Mac Mini's power cord. Hold down the power button for 5 seconds.

Step

Release the power button. Reconnect the power cord.

Step

Press the power button to turn on the computer.

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Here's how to reset your PRAM:

Shut down your machine. Yes, all the way down, not sleep or logging out.

Press the power button and then press command-option-p-r. ...

Hold those keys down until your Mac reboots again and you here the startup chime.